BarContainer properties and attributes

BarContainer gained a new widths property. It returns a list of the widths of the individual bars in the container (the dimension perpendicular to the bar height).

For standard bar plots (e.g. created by Axes.bar or Axes.barh), this reflects the width of each bar in the plot. For grouped bar plots (e.g. created by Axes.grouped_bar), each BarContainer represents one group of bars across categories, so widths returns the width of each individual bar in that group, rather than the total width of the entire group.

Additionally, BarContainer gained a new group_positions attribute, which exposes the center positions of the bar groups if the container is part of a grouped bar plot (e.g. created by Axes.grouped_bar), or None otherwise.